I was listening to music while on the bus, and I was just a bit zoned out and looking in a random direction. Turns out I'd been staring at a girl's ass for about 2 minutes before realising.
I then look in a different direction, and an old woman, who was sitting besides the girl I'd just been staring at, winks at me as if she'd seen me stare for the full 2 minutes. I then had to stand embarrassed in the bus for 10 more minutes before it was my stop.